1. Field of the Invention
This invention relates to an image display system, an image display method and an image display apparatus and, more particularly, it relates to an image display system comprising a plurality of image signal sources and an image display apparatus.
2. Related Background Art
As a result of the development in the field of communication technologies in recent years, more and more communication networks are currently installed in offices. Printers, scanners and other electric devices are mutually connected by way of personal computers (to be referred to as PCs hereinafter) in many offices. Additionally, communication systems for connecting home electric devices such as HAVi (home audio/video interoperability) and Jini by means of networks have been standardized by IEEE (Institute of Electrical and Electronics Engineers, Inc.) 1394 and USB (Universal Serial Bus) to promote the utilization of such systems.
Furthermore, arrangements for transmitting video signals from a PC to a large screen plasma display or a large screen projector for the purpose of presentation and/or TV conferencing in order to allow access to various data are already in place in many offices. Similarly, arrangements for transmitting video signals from a DVD to a television set adapted for a wide screen (to be referred to as TV hereinafter) or a large screen rear projection TV for the purpose of showing films and home videos are also already in place in a number of homes.
Under these circumstances, TV monitors and PC displays are required to display images of the video signals output from electric devices connected thereto by way of networks. Recently, TV monitors and PC displays that are compatible with each other have been marketed so that an image transmitted from a PC now can be displayed on a TV monitor and vice versa.
FIG. 10 of the accompanying drawings schematically illustrates the internal configuration of a known popular image display system of the type under consideration. In FIG. 10, a PC 100 and a PC display 600 are connected to each other by way of transmission lines 114a, 114b. 
The PC 100 comprises a DDC (display data channel) communication section 110 for receiving the video signal transmitted from the PC display 600, a main memory section 104 contained in the main body of the PC 100, a recording medium section 105 for storing information in and reproducing information from a recording medium that may be a hard disk, a graphics drawing section 106 for producing an image signal on the basis of the received video signal and various pieces of information stored in the main memory section 104 and the recording medium section 105, an image memory 107 which is used by the graphics drawing section 106 for producing an image signal, an image transmitting section 108 for transmitting the image signal produced from the graphics drawing section 106 to the PC display 600, a bus control section 103 for monitoring and controlling the data bus 111a connecting the above sections and a CPU (central processing unit) 102 for control the operation of the PC main body 100.
The PC 100 comprises a connection line 111b connecting the CPU 102 and the bus control section 103, a connection line 111c connecting the DDC communication section 110 and the graphics drawing section 106, a connection line 111d connecting the graphics drawing section 106 and the image transmitting section 108 and a connection line 111e connecting the graphics drawing section 106 and the image memory 107.
On the other hand, PC display 600 comprises an image receiving section 218 for receiving the image signal transmitted from the image transmitting section 108 and typically conforming to the TMDS Standards and converting its format into one adapted to processing the signal comprising 8-bit for each of the primary colors of RGB, a format converting section 219 for converting the format of the image signal from the image receiving section 218 in terms of resolution, frame frequency and so on in order to make the image signal match the number of display pixels of the main body of the PC display 600, an image memory section 220 to be used for converting the format of the image signal, an image processing section 221 for processing the format-converted image signal in terms of gamma characteristics and color characteristics, an image display section 222 typically comprising a liquid crystal display, a CRT, a PDP, an EL display or an LED display, a DDC for transmitting a video signal to the PC 100 and a microcomputer section 217 for controlling the main body of the PC display 600.
The microcomputer section 217 by turn comprises a resolution determining section 223 for receiving information (including the frequency and the polarity of the synchronizing signal) on the image signal received by the image receiving section 218, determining the resolution of the received image and transmitting a control signal to be used for converting the format of the image signal to the format converting section 219.
The PC display 600 additionally comprises a connection line 225b connecting the image receiving section 218 and the format converting section 219, a connection line 225e connecting the format converting section 219 and the image memory 220, a connection line 225c connecting the format converting section 219 and the image processing section 221, a connection line 225d connecting image processing section 221 and the image display section 222 and a data bus 225a connecting the microcomputer section 217 and the sections 218, 219, 221, 222 and 224.
As seen from FIG. 10, in the known popular image display system, the PC 100 and the PC display 600 are connected to each other not by means of a network but by way of transmission lines 114a, 114b to establish a 1 to 1 connection. Then, the image resolution is determined as a result of the exchange of EDID data between the DDC communication sections 224 and 110 that takes place when the PC is activated or in the operation of detecting the connection of the PC 100 and the PC display 600 so that the resolution is appropriately converted in the PC display 600 before displaying the image according to the input video signal.
It should be noted here that the PC is the host of the system and the PC display serves the host. For example, when the PC and the PC display determine the resolution of the image to be displayed, only a list of resolutions that can be used for displaying the image as defined in the Extended Display Identification Data Standard, Version 3, is transmitted from the PC display to the PC by DDC communication and the actual resolution is determined by the graphics drawing section of the PC after referring to the list. Then, the PC arbitrarily outputs the image signal with the determined resolution to the PC display. Therefore, the PC display has to find out the resolution from the transmitted image signal and perform an appropriate resolution converting operation on the input image signal. This process of determining the resolution by DDC communication is based on the fact that the PC controls the display area of the PC display as host. In short, known image display systems of the type under consideration are not adapted to connect a plurality of PCs and a PC display in such a way that images represented by the image signals transmitted from some or all of the PCs are simultaneously displayed on the PC display.
FIG. 11 is a schematic illustration of a system such as HAVi or Jini connecting a number of home AV devices and comprising an image display system as shown in FIG. 10.
Referring to FIG. 11, there are shown a public communication network 395, a modern 394 connected to the public communication network 395, IEEE 1394 hubs (HUBs) 387, 388 for sorting and delivering IEEE 1394 signals, various electric devices connected to the IEEE 1394 hubs 385, 386, 399, 313, 380, 391, 392 and a set top box (STB) connecting a digital television set 301 and the IEEE 1394 hub 307.
It should be noted here that digital television set 313 contains an IEEE 1394 decoder and hence is connected directly to the IEEE 1394 hub 388 without using a set top box.
In FIG. 11, there are also shown communication lines 17a through 17i conforming to the IEEE 1394 Standard and connecting the electric devices and the corresponding IEEE 1394 hubs 387, 388 and also mutually the IEEE 1394 hubs, a connection line 17j connecting the modem 394 and the IEEE 1394 hub 388, a connection line 16 which is typically a telephone line connecting the modem 394 and the public communication network 395, a cable 19 dedicated to images and having a D terminal connecting the set top box 382 and the digital television set 301 and cables 18b, 18a dedicated to images and connecting the PCs 380, 399 and the PC displays 309, 383 respectively.
The various electric devices shown in FIG. 11 include digital television sets (DTVs) 301, 313 adapted to receive digital broadcasts, a separate digital television tuner (DTV Tuner) 385, a digital video set (DV) 386, PCs 380, 399, PC displays 309, 383 connected to the respective PCs, a DVD player (DVD) 391 and a hard disk drive (HDD) 392 for recording broadcast programs.
Note that the PCs 380, 399, the PC displays 309, 383 and the cables 18b, 18a dedicated to images that are shown in FIG. 11 correspond respectively to the PC 100, the PC display 600 and the transmission lines 114a, 114b described earlier by referring to FIG. 10.
With the IEEE 1394 network illustrated in FIG. 11, the user can realize an environment where he or she can display images represented by respective image signals transmitted from some or all of the various electric devices 385, 386, 391, 392 on the display screens of the digital television sets 301, 313. Such a system can be realized because the digital television sets 301, 313 operate as hosts that use image signal sources including the DVD 391 and the DV 386 as slaves and control the operation of allocating the virtual display areas (e. g., channels and window positions of a multiple screen) of TVs to some or all of the image signal sources and hence the image signal sources do not have the right of specifying the respective display positions.
On the other hand, while the PCs 380, 399 are connected respectively to the IEEE 1394 hubs 388, 387, signal transmissions and receptions conforming to the IEEE 1394 Standard do not take place between the PCs 380, 399 and the respective PC displays 309, 383. In other words, the image signals from the DVD 391 and the DV 386 and those from the PCs 380, 399 cannot coexist on the network.
The above described known technology is not adapted to connect a plurality of PCs to a common image display apparatus and display the images represented by the image signals from the respective PCs on the display screen of the image display apparatus. Furthermore, it is not adapted to allow image signals from TV sets and those from PCs to coexist on the network.
However, the entire cost of the system will be high and resources will be wasted when the plurality of PCs of the system are provided with respective image displays as PC displays and image signals from the TVs and those from the PCs are not allowed to coexist on the network. Therefore, there will be a strong demand for a system where a plurality of PCs are connected to a single common image display apparatus so that the images represented by the image signals from various image signal sources including some or all of the PCs may be displayed on the display screen of the image display apparatus.
On the other hand, the inventor of the present invention have found that appropriate measures need to be taken when the images represented by the image signals from a pair of PCs are to be displayed on the display screen of an image display apparatus because, otherwise, the image signals from the pair of PCs coexist in the image memory in an disorderly fashion and the images can be displayed in an overlapping manner. Then, the overlapping areas of the images will flicker to severely damage the quality of the displayed images.
The inventor of the present invention tried to transmit only the data for the difference between a preceding image signal and a succeeding image signal for updating the preceding image signal by partially rewriting it in an attempt of reducing the volume of data to be transmitted as image signal by way of a communication network. As a result, the inventor of the present invention found that two image data indicating a same coordinate system are input alternately to a signal decoder to be used for the partial rewriting operation. The net result is that the image obtained and displayed on the display screen of an image display apparatus can be a disorderly mixture of two images because the decoding circuit for indicating the coordinate system does not operate properly. Therefore, it may not be possible to display the intended image with such a technique.
The above identified problem does not arise in a system where TV-related devices are connected because the TV set operates as host for displaying images. However, in the case of PC-related devices connected to a common display device, the display device cannot respond properly to the signals transmitted from a number of host devices and indicating the respective display attributes such as display coordinates particularly when the signals contain contradictory factors.
In view of the above identified circumstances, it is therefore the object of the present invention to realize a system where a plurality of image signal sources such as PCs are connected to a single and common image display apparatus and the image display apparatus can display the images represented by the image signals transmitted from some or all of the image signal sources in an orderly manner without disorderly mixing of the images.
In an aspect of the invention, there is provided an image display system comprising:
a plurality of image signal sources adapted to respectively transmit image signals and pieces of display area information specifying the display areas of the respective images represented by the image signals; and
an image display apparatus adapted to display the images on its display section according to the transmitted pieces of display area information;
said image display apparatus having:
a determining section for determining the presence or absence of an overlapping area on the display section on the basis of said pieces of display area information transmitted from said image signal sources; and
an erasing section for erasing the image signal of the image to be displayed behind the other image for the overlapping area as determined to exist by said determining section.
In another aspect of the invention, there is provided an image display system comprising:
a plurality of image signal sources adapted to respectively transmit image signals and pieces of display area information specifying the display areas of the respective images represented by the image signals; and
an image display apparatus adapted to display the images on its display section according to the transmitted pieces of display area information;
said image display apparatus having:
a determining section for determining the presence or absence of an overlapping area on the display section on the basis of said pieces of display area information transmitted from the said image signal sources; and
a processing section for processing either of the pieces of display area information of the images to be overlapping so as to eliminate the overlapping area as determined to exist by said determining section and display the images without overlapping.
In still another aspect of the invention, there is provided an image display method adapted to receive image signals and pieces of display area information specifying the display areas of the respective images represented by the image signals transmitted from a plurality of image signal sources by means of an image display apparatus and display said images on a display section of said image display apparatus according to the respective pieces of display area information, said method comprising:
a step of determining the presence or absence of an overlapping area on the display section on the basis of said pieces of display area information transmitted from said image signal sources; and
a step of erasing the image signal of the image to be displayed behind the other image for the overlapping area as determined to exist by said determining section.
In still another aspect of the invention, there is provided an image display method adapted to receive image signals and pieces of display area information specifying the display areas of the respective images represented by the image signals transmitted from a plurality of image signal sources by means of an image display apparatus and display said images on a display section of said image display apparatus according to the respective pieces of display area information, said method comprising:
a step of determining the presence or absence of an overlapping area on the display section on the basis of said pieces of display area information transmitted from said image signal sources; and
a step of processing either of the pieces of display area information of the images to be overlapping so as to eliminate the overlapping area as determined to exist by said determining section and display the images without overlapping.
In still another aspect of the invention, there is provided a recording medium storing a program including instructions for causing a computer to execute either of the above image display methods.
In a further aspect of the invention, there is provided an image display apparatus adapted to display a plurality of images on a display screen thereof in an overlapping manner, said apparatus comprising:
an input section for linking the image display apparatus and a plurality of external image signal sources by way of a communication network;
a determining section for determining the presence or absence of an overlapping area of the images from any two of said plurality of external image signal sources before displaying the images on said display screen; and
an erasing section for erasing the image signal of the image to be displayed behind the other image for the overlapping area as determined to exist by said determining section.
In still another aspect of the invention, there is provided an image display apparatus adapted to display a plurality of images on a display screen thereof in an overlapping manner, said apparatus comprising:
an input section for linking the image display apparatus and a plurality of external image signal sources by way of a communication network;
a determining section for determining the presence or absence of an overlapping area of the images from any two of said plurality of external image signal sources before display the images on said display screen; and
a processing section for processing either of the pieces of image information of the images to be overlapping so as to eliminate the overlapping area as determined to exist by said determining section and display the images without overlapping.